The present invention relates generally to stability control systems for vehicles, and more particularly relates to the determination of a direction of travel of the vehicle.
Some modern vehicles utilize a stability control system for controlling advance vehicle dynamics. Such stability control systems require a determination of the direction of travel for many purposes, including: 1) disabling of stability control while traveling in reverse; and 2) recognizing the steering wheel angle in a turn only when traveling forwardly. Most systems rely almost 100% on the transmission gear position given by the gear selector (PRNDL) to determine the direction of travel.
Unfortunately, the indication from the transmission gear position is not always accurate. For example, the switch utilized at the gear selector can be broken. At times, the gear selector can be between gears, and the switch will give a toggling readout that is inaccurate. Still further, the transmission gear position may be in neutral, although the vehicle may be moving forwardly or rearwardly, i.e. when the vehicle is rolling on a hill. Accordingly, there exists a need to provide a determination of the direction of travel that is less dependent upon the transmission gear position.
The present invention provides a method of determining the direction of travel that is independent of the transmission gear position. This method allows for the rapid detection of the travel direction, even if the driver""s steering wheel input is very small and the vehicle velocity is low. Furthermore, reliance on the transmission gear position is minimized, and the gear position is only used to increase the confidence of the determined direction of travel.
Generally, a plurality of yaw (turning) rate values is utilized, which are summed over a period of time. Preferably, the yaw rate values are integrated over time at discrete intervals. A plurality of yaw rate sum values are generated, and the sign of each yaw rate sum value is compared. This comparison of the signs of each yaw rate sum value results in a confidence value that is used to determine the direction of travel. Preferably, the actual gear position, a calculated gear ratio, and the vehicle""s velocity are used to build confidence in the resulting confidence value.